I'm bored. Let's plan a manned Venus landing.

[Themohawkninja]

4kw wind turbine, if the atmosphere is more dense then with more force pushing the blades you could probably scale it down and still achieve 4kw. The only problem is trying to fit it into a constrictive design, wind turbines aren't small...

Potential for deployable turbines?

If the radially attached struts that attach the "blades" to the main shaft were re-designed to be at a right angle with the shaft, than they could be retractable.

[MBobrik]

Potential for deployable turbines?

from

http://www.universetoday.com/36816/winds-on-venus/

At the very top of the cloud layers on Venus, wind speeds reach 355 km/hour (or 100 meters/second). This is the same the jet stream here on Earth. As you descend through the cloud layers, though, the wind speeds pick up. In the middle layer, the winds can reach speeds of more than 700 km/hour. That’s faster than the fastest tornado speed ever recorded on Earth.

But then as you descend further down through the clouds, the thickening atmosphere slows the winds down, so that they act more like currents in the ocean than winds in the atmosphere. Down at the surface, the winds only move at a few km/hour. That’s not much, but the thick atmosphere can still kick up dust and push around small rocks.

from

http://hyperphysics.phy-astr.gsu.edu/hbase/solar/venusenv.html

.

Above the clouds there is a high-speed "jet stream" which blows from west to east at about 300-400 km/h. This wind is fastest at the equator and slows toward the poles, often giving a "V" type pattern in the visible cloud cover. At the surface there is almost no prevailing wind, with measured surface wind speeds typically less than 2 m/s.

.

Maybe there could be a reasonably sized wind turbine ( shaped more like a water propeller because of the atmosphere thickness ) could supply the required energy even with wind speeds of only 2 m/s, but any prolonged calm would result in cooked astronauts.

[Kryten]

How about geothermal (Well, hermethermal)?

[MBobrik]

How about geothermal (Well, hermethermal)?

You would have to drill a lot to get hot enough to have a meaningful temperature gradient relative to a 750 K atmosphere.

I think that the best solution is a high-temperature plutonium reactor. Plutonium has a critical mass of mere EDIT:10 kg ( even less with a beryllium reflector ) using the locally available supercritical CO2 as coolant and working fluid. You wouldn't need to worry about shielding, the 60 kg/m3 dense atmosphere will do the job fine all on its own, just hold the reactor on a long pole away from the crew quarters.

.

One more thing. the 4kw value is most probably overrated. I took the thermal conductivity of the best insulation available with thermal conductivity of 0.006 W /K /m2 I came with like 300 W for a 9 m diameter sphere and 450 K temperature gradient.

Edited June 21, 2013 by MBobrik

[nhnifong]

You would have to drill a lot to get hot enough to have a meaningful temperature gradient relative to a 750 K atmosphere.

I think that the best solution is a high-temperature plutonium reactor Plutonium has a critical mass of mere 3 kg ( even less with a beryllium reflector ) using the locally available supercritical CO2 as coolant and working fluid. You wouldn't need to worry about shielding, the 60 kg/m3 dense atmosphere will do the job fine all on its own, just hold the reactor on a long pole away from the crew quarters.

I think it's probably an even toss-up between a plutonium reactor + turbine for the heated C02, and a collapsible vertical wind turbine.

What do you think a reactor designed for about 1 kW would weigh?

One more thing. the 4kw value is most probably overrated. I took the thermal conductivity of the best insulation available with thermal conductivity of 0.006 W /K /m2 I came with like 300 W for a 9 m diameter sphere in diameter and 450 K temperature gradient.

I would not be surprised. I was a bit confused about that math.

Which insulation are you talking about anyways?

[MBobrik]

The plutonium would weight around 3 Kg but you would need some more Kg of neutron moderator around, beryllium carbide is the material of choice, which is lightweight and efficient. So, say, the entire reactor w/o shielding, turbine and cooler would weight around 20-30 Kg. Together it may be below 100 Kg, conservative estimate.

.

EDIT : The best insulation available

[Kryten]

I think it's probably an even toss-up between a plutonium reactor + turbine for the heated C02, and a collapsible vertical wind turbine.

What do you think a reactor designed for about 1 kW would weigh?

Smallest reactor I can find with reasonable amounts of info is the soviet Buk, flown on a set of radar sats; 3KW electrical power for 130kg weight without shielding, but with colling system. That's with thermoelectric conversion, turbine could probably get quite a lot more out of it; thermal output was 100KW

EDIT: That's also including a system to eject the reactor core, and I'm pretty sure the actual converter.

Edited June 21, 2013 by Kryten

[MBobrik]

3KW electrical power for 130kg weight without shielding, but with colling system. That's with thermoelectric conversion, turbine could probably get quite a lot more out of it; thermal output was 100KW

.

You won't need any cooling when you are immersed in hot supercritical CO2. Just go open-cycle, suck in CO2 from bottom solely through buoyancy, and above the reactor core a lightweight turbine propelled by the rising buoyant CO2 before being released back to the atmosphere. The Venussian Greenpeace would not be happy about the rising radioactive plume, but, of course, there is no Venussian Greenpeace

[nhnifong]

Since we are considering not just an RTG, but a supercritical CO2 turbine, and we're thinking of using it to power a heat pump, and supercritical CO2 is an excellent refridgerant fluid, maybe somehow we can combine all the necessary machines here into one big turbine that simultaneously generates power, pumps heat out of ship, and produces an exhaust supercritical fluid stream that can be directed to produce thrust, or run the ship as a hovercraft. All powered by a couple kilos of Plutonium In space it would run as a closed cycle system (except while thrusting), venting heat using radiators, and on Venus, it would switch to an open cycle and just pump ambient supercritical CO2 from the atmosphere.

Supercritical CO2 is awesome!

Edited June 21, 2013 by nhnifong

[MBobrik]

maybe somehow we can combine all the necessary machines here into one big turbine that simultaneously generates power, pumps heat out of ship, and produces an exhaust supercritical fluid stream that can be directed to produce thrust, or run the ship as a hovercraft

What about a plutonium fueled helicopter ? Turbine, CO2 pump, power generator and heat pump on one shaft, and the helicopter rotor driven through a gearbox.

EDIT : Even crazier and simpler design. screw turbine, pump and gearbox. Make the rising plume of superheated CO2 spread and draw with it upwards a lot of ambient CO2. Then place a large helicopter rotor above it. It will spin up and you will be able to fly solely through induced autorotation ( and will even be able to drive the heat pump and generator with it )

Edited June 21, 2013 by MBobrik

[nhnifong]

Can the heat pump not only be on the same shaft, but actually share working fluid with the turbine? meaning that only one compressor would be needed?

[MBobrik]

Working fluid would be the same ambient CO2 that is all around. The heat pump will be open-cycle too.

[nhnifong]

I guess I'd need to learn more about supercritical CO2, but I'm confused about just how the heat pump should best be incorporated into the turbine. If this turbine is anything like a regular old jet turbine, the compressor draws in fluid, the plutonium heats it up, then it's decompressed and spins the turbine as it exits at a lower pressure but higher temperature. Is the fluid decompressing in the turbine going to also draw heat from components it comes in contact with, such as helium tubes along the walls of the chamber?

Is a supercritical refrigerator anything like a vapor compression cycle refrigerator? or would it be more like an absorption refrigerator because there are no phase changes to cross? perhaps the compressed CO2 needs to be split into two streams just after the compressor. one stream is heated by the plutonium and drives the turbine, and the other stream is decompressed to absorb heat from the radiator of the habitat's low-temp heat pump.

Maybe I'll make a diagram

[MBobrik]

The supercritical working fluid has to expand to cool down below ambient temperature just like a gas does, because there is no phase change involved. So, the open cycle heat pump would be little more than a vacuum pump that keeps a tube at low pressure at one end and a small opening that sucks in ambient CO2 and lets it expand on the other.

[Kryten]

Isn't CO₂ quite strongly oxidising at elevated temperatures? Running it through a reactor core might not be the best idea.

[MBobrik]

Isn't CO₂ quite strongly oxidising at elevated temperatures? Running it through a reactor core might not be the best idea.

The standard reaction goes like 2CO <-> CO2 + C. temperature shifts the equilibrium to the left, pressure to the right.

I am sure that say 2000 K would be enough to shift the equilibrium even at 93 MPa so far to the left that even reactions like CO2 + M -> CO + MO ( where M means any metal ) would proceed quite rapidly, but if the surface of your reactor is nothing but refractory oxides like PuO2 and BeO, then you have nothing to worry about oxidation at all - everything that could be oxidized already is...

[Kryten]

Pretty sure that puts up reactor weight quite a lot though. Design I posted is nearly pure metallic U²³⁵.

[MBobrik]

Pretty sure that puts up reactor weight quite a lot though.

I was talking about the surface. The fuel rod interior could be pure ( at the working temperature liquid ) plutonium. Only the outer shell holding it together would be oxide.

[nhnifong]

Has there been any prior attempt to contain liquid plutonium? How do you control the reaction rate? do the usual neutron absorbing rods do the trick or would they just melt?

[Tarrow]

Randomish thought for EVA's - would it be possible to offset the heavy atmospheric pressure by shifting to a liquid based breathing apparatus such as has been proposed for deep diving (as used in "The Abyss")? Would also provide a fairly sizable body contact area for thermoregulation. iirc the biggest issue to using it at the moment is that the required flow rate for perfluorocarbons is fairly high (about 10l a minute) but that'd be solvable surgically.

Ok so it's more complex than a hardsuit, but it'd weigh little more than the equivalent of a hazmat suit and rebreather and there'd be no need for exoskeleton assist.

Has there been any prior attempt to contain liquid plutonium?

Containment / storage of liquid plutonium is fairly easy tbh. It's melting point of around 640c is about half that of stainless steel. Boron carbide (melting point 2678c) could be used as a neutron absorber quite nicely I would think.

Edited June 23, 2013 by Tarrow

[Geo793]

The lander should be spherical in shape, possibly made out of Pyrex which is resistant to strong acids, high temperatures, and extreme pressure. If te crew is planning on living on venus for an extended period of time (more than 3-4 years), they should use drilling equipment to produce a larger base under the surface and away from the hostile environment.

[MBobrik]

Ok so it's more complex than a hardsuit, but it'd weigh little more than the equivalent of a hazmat suit and rebreather and there'd be no need for exoskeleton assist.

.

EDIT : I've been corrected, the pressure is only 9.2 MPa. so my conclusions are most likely wrong, but the idea of adding arms and legs to your lander making it in effect a gigantic walking robot is cool anyway

.

I don't think that EVA is possible. Because water chemistry changes slightly with pressure, you can't stand 93 MPa, chemical reactions inside your cells would go haywire and you would just die long before that pressure.

.

So your EVA suit would have to keep both the pressure and temperature outside making its surface dozens of cm thick. It would look like an enormous boiler with short and thick arm and leg stubs. No chance of anything resembling normal human movement with this. You might as well as attach huge robotic legs and arms to your lander and declare it to be your spacesuit

.

Edited June 24, 2013 by MBobrik

[MBobrik]

Has there been any prior attempt to contain liquid plutonium? How do you control the reaction rate? do the usual neutron absorbing rods do the trick or would they just melt?

.

Molten plutonium can be handled in a refractory ceramic crucible just like any molten metal. Even the plutonium oxide is a good refractory material on its own, so plutonium can be held in a outer shell of its own oxide !

.

And generally, all other materials you need, beryllium oxide moderator, boron carbide, are refractory compounds. And the best is yet to come. Because the supercritical CO2 flowing through the reactor does a large part of the moderation, the reactor will be passively stable ( capable of maintaining a stable state w/o any control rod adjustments ) because of the negative feedback from decreasing moderator density with temperature.

[Tarrow]

.

I don't think that EVA is possible. Because water chemistry changes slightly with pressure, you can't stand 93 MPa)

There's a fairly important issue in that 93 MPa as Venus' quoted surface pressure is incorrect by an order of magnitude. Most resources (from wikipedia up to more reliable, printed, sources) have the surface pressure at around 9000 kPa (9 MPa) - or 93 bar. That's only thee times the pressure at which scuba divers have operated using conventional compressed-gas respiration.

secondary random thought (nuclear reactors) - make the fuel self moderating. The fuel assemblies proposed for a pebble bed style reactor become less energetic as temperature increases, with a peak self-heating temperature below the failure temperature of their own structure. Remove the control rods completely from the equation - they're just another failure point where human error can cause problems.

Edited June 24, 2013 by Tarrow

[MBobrik]

There's a fairly important issue in that 93 MPa as Venus' quoted surface pressure is incorrect by an order of magnitude. Most resources (from wikipedia up to more reliable, printed, sources) have the surface pressure at around 9000 kPa (9 MPa) - or 93 bar. That's only thee times the pressure at which scuba divers have operated using conventional compressed-gas respiration.

.

I checked it, and you are right. the pressure is not 93 MPa but only 9.2 MPa. That makes EVA at least theoretically possible at ambient pressure. you would, however still need to wear pretty thick and heavy thermal protection. But at least we are moving from utterly impossible to possible with difficulties.